1. Field of the Invention
The present invention relates generally to tire monitor systems, more particularly to tire monitor system sensors and methods employing a tire valve antenna, and specifically to coupling of such antennas with sensor unit circuitry.
2. Description of the Prior Art
A tire monitor system monitors various tire conditions such as tire pressure and/or temperature and informs a driver of such conditions, particularly excessively high or low pressures or excessively high temperatures. A radio frequency (RF) transmission is typically used to remotely transmit tire pressure information to a central vehicle computer or the like, which in turn, conveys the information to the driver, via a dashboard display, warning light, audible warning signal, or the like. Some tire monitor system sensor units include a tire pressure detector deployed in conjunction with a more-or less typical tire valve. The tire pressure detector typically includes one or more sensors such as a pressure sensor, an RF transmission circuit, a control circuit, a power source such as a battery, etc. The pressure sensor measures tire pressure and produces a signal related to the measured tire pressure. The signal may be used by the control circuit to produce tire condition information. Some tire pressure sensor units are secured to a wheel rim using the tire valve. Examples of such “snap-in” tire pressure sensor units are disclosed in U.S. Pat. Nos. 6,005,480 and 6,163,255.
To transmit tire condition information, conventional tire pressure sensor units may employ an external planar antenna, or the like. An external antenna increases the weight of the tire pressure sensor unit. The battery is often the heaviest component in the tire pressure sensor unit. Because of the forces of rotation of the wheel and tire pressure sensor unit, the tire pressure sensor unit is carefully designed to balance the weight of other components against the battery. An external planar antenna mounted on the tire pressure sensor unit may impair the balance and require that the tire pressure sensor unit be designed around the bulk of the antenna as well as the weight of the battery. Further, the resultant tire pressure sensor unit may not be as compact and/or lightweight as is desirable.
Problematically, the signal transmitted by a sensor having an antenna disposed inside a tire mounted on a wheel is greatly attenuated. Therefore, some existing tire pressure sensor units employ the tire valve stem as an antenna. However, such sensors usually integrate the tire valve and the sensor housing, or at least permanently secure the tire pressure sensor housing and stem together and/or typically permanently wire the sensor circuitry to the valve stem. Therefore, the entire sensor and valve stem unit must be replaced as a single unit, when only the relatively inexpensive tire valve needs to be replaced.